The BEST key performance indicator (KPI) to measure the effectiveness of a vulnerability remediation program...

 According to the Key Performance Indicators for Vulnerability Management article, the number of vulnerabilities remediated is a key performance indicator that measures the effectiveness of a vulnerability remediation program. This KPI indicates how many vulnerabilities have been successfully mitigated or fixed within a given time frame. A higher number can imply that the organization is effectively managing its exposures and reducing its risk level. The number of vulnerabilities remediated can also be compared with the number of new vulnerabilities identified to evaluate the progress and performance of the vulnerability remediation program. References = Key Performance Indicators for Vulnerability Management